Narrative:

I fly an aircraft with an IFR-certified garmin GNC300XL; which is a non-waas GPS receiver. We have been noticing lately that this unit is drawing incorrect courses from our present position direct to GPS waypoints. Sometimes the unit will draw the correct course; and while we are enroute on that course; it will completely re-draw an incorrect route to the same waypoint. Sometimes the unit will completely delete all waypoint information and leave us with no course to follow whatsoever; as though the unit has just been initialized and is waiting for us to input information.while enroute to our destination airport on a VFR training flight; the unit erased our course and waypoint while we were 15 miles southwest of the destination. We simply reverted to pilotage to continue to our destination airport.this could; however; present a real problem to GNC300XL operators; especially during IFR conditions; hence the reason for this report. While searching for the solution to this problem; we are limiting the unit for use during VFR operations only.

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Original NASA ASRS Text

Title: An IFR-certified Garmin GNC300XL installed in a C150 began giving faulty information related to courses and waypoints.

Narrative: I fly an aircraft with an IFR-certified Garmin GNC300XL; which is a non-WAAS GPS receiver. We have been noticing lately that this unit is drawing incorrect courses from our present position direct to GPS waypoints. Sometimes the unit will draw the correct course; and while we are enroute on that course; it will completely re-draw an incorrect route to the same waypoint. Sometimes the unit will completely delete all waypoint information and leave us with no course to follow whatsoever; as though the unit has just been initialized and is waiting for us to input information.While enroute to our destination airport on a VFR training flight; the unit erased our course and waypoint while we were 15 miles southwest of the destination. We simply reverted to pilotage to continue to our destination airport.This could; however; present a real problem to GNC300XL operators; especially during IFR conditions; hence the reason for this report. While searching for the solution to this problem; we are limiting the unit for use during VFR operations only.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.